13. Queue Management Policies

This chapter provides information to configure queue management policies using the CLI.

13.1. Overview

A set of profiles or templates are available in hardware for configuring the queue parameters, such as CBS, MBS, and WRED slopes. These profiles are available for use with multiple queues on the system. Queue management policies allow the user to define the queue parameters and allow sharing among the queues.

A single system buffer pool is available for use by all the queues on the system. Users can allocate the amount of buffers that each queue can use by specifying the CBS and MBS parameters in the queue management policy.

Weighted Random Early Detection (WRED) is available to manage buffers during periods of congestion. WRED slopes are supported for each queue in the system. Queue management policies allow the user to configure slope parameters that dictate a WRED profile for each queue. Each queue supports the following slopes:

  1. slope for in-profile or high priority traffic
  2. slope for out-of-profile or low priority traffic

Each slope allows users to specify the start average, the max average, the drop probability and the Time Average Factor (TAF). Each queue has a default slope policy. Multiple queues in the system can share a single policy. If a policy is shared, the system computes the WRED drop probabilities for each of the queues separately based on their average queue length.

13.2. Basic Configurations

A basic queue management policy must conform to the following restrictions.

  1. Each slope policy must have a unique policy ID.
  2. High slope and low slope are shut down by default.
  3. Default values can be modified but parameters cannot be deleted.

13.2.1. Creating a Queue Management Policy

To create a new queue management policy, define the following:

  1. a queue management policy name
  2. a brief description of the policy features
  3. CBS and MBS values for default queue management policy
  4. high slope for the high priority WRED slope graph
  5. low slope for the low priority WRED slope graph
  6. time average factor (TAF)
  7. slope parameters, such as max-avg, start-avg, max-prob, time-average-factor

Use the following syntax to configure a queue management policy.

CLI Syntax:
config>qos
  queue-mgmt name
    description description-string
    cbs kbytes
    mbs kbytes
    high-slope
        start-avg percent
        max-avg percent
        max-prob percent
        no shutdown
    low-slope
        start-avg percent
        max-avg percent
        max-prob percent
        no shutdown
      time-average-factor taf

The following is a sample queue management policy configuration output.

A:7210>config>qos>queue-mgmt# info 
  
     ----------------------------------------------
                high-slope
                    shutdown
                    start-avg 40
                    max-avg 50
                exit
                low-slope
                    shutdown
                    start-avg 40
                    max-avg 80
                exit
            cbs 5000
            mbs 800000
        time-average-factor 7
       ----------------------------------------------

13.2.2. Editing QoS Policies

Existing policies and entries can be edited using the CLI or NMS. The changes are applied immediately to all services where the policy is applicable.

To prevent configuration errors, perform the following.

  1. Copy the policy to a work area.
  2. Edit the policy.
  3. Overwrite the original policy.